参考MOS：
在Linux 环境下Oracle 9i，10g，11gR1 的RAC 需要配置Hangcheck_timer模块。
Note : Hangheck timer is notrequired starting with Oracle Clusterware 11gR2
Starting in release 9.2.0.2and later, Oracle RAC environments required using a new I/O fencing model,named the hangcheck-timer module. This module was implemented to replace theWatchdog module, which provided similar fencing functionality. Hangcheck-timerwas subsequently delivered as part of the standard kernel distribution forLinux kernel releases 2.4 and above.
从9.2.0.2版本开始，ORACLERAC环境需要使用一个新的I/O fencing模块，叫做hangcheck-timer模块。这个模块用来代替Watchdog模块，提供类似的fencing功能。Hangcheck-timer模块是标准的linux2.4以上的内核中的一个子功能被发布。
Hangcheck-timer shouldbe loaded at boot time, and monitors the Linux kernel for long operatingsystem hangs that could affect the reliability of a RAC node. It runs inkernel mode and uses the Time Stamp Counter (TSC) to catch scheduling delays ornode hangs. This is done by setting a timer, then checking when the timerfires as to whether it was delayed by more than the allowed margin oferror. If the duration exceeds the allowed time of (hangcheck_tick +hangcheck_margin seconds), the machine is restarted. Hangcheck-timer willnot cause reboots to occur due to CPU starvation.
--Hangcheck-timer应该在系统启动的时候被加载, 并对于能够影响RAC节点稳定性的长时间的系统操作HANG进行内核监控。它运行在内核级别并使用Time Stamp Counter(TSC)来捕捉调度的延迟和节点HANG。这是通过设置一个timer，然后检查这个timer的fires情况来判断是否延迟是否超过了误差的幅度。如果这个周期超过了允许的时间（也就是hangcheck_tick+hangcheck_margin秒），机器将会被重启，如果是CPU资源不足的时候，Hangcheck-timer将不会导致重启。
Hangcheck-timer requiresthree configuration parameters:
--Hangcheck-timer有三个配置参数:
(1) hangcheck_tick - defines howoften, in seconds, the hangcheck-timer checks the node for hangs. The defaultvalue is 60 seconds.
-- hangcheck_tick：定义了hangcheck-timer检查节点是否hang的频率，单位是秒，缺省是60秒.
(2) hangcheck_margin - defines howmuch margin is allowed, in seconds, between expected scheduling and realscheduling time. The default value is 180 seconds.
--hangcheck_margin：定义期望的和真正的scheduling之间允许的误差，单位是秒，缺省值是180秒.
(3) hangcheck_reboot - determinesif the hangcheck-timer restarts the node if the kernel fails to respond withinthe sum of the hangcheck_tick and hangcheck_margin parameter values. If theva lue of hangcheck_reboot is equal to or greater than 1, then thehangcheck-timer module restarts the system. If the hangcheck_reboot parameteris set to zero, then the hangcheck-timer module will not reboot the node,even if a hang is detected. The default value varies by kernelversion. In the 2.4 kernel, the default is 1. In 2.6 kernels, thedefault is 0.
--hangcheck_reboot：定义了如果内核在hangcheck-tick和hangcheck-margin相加的时间内响应失败的话，hangcheck-timer是否重启节点。如果hangcheck_reboot的值大于等于1,hangcheck-timer模块将会重启系统；如果设置为0，则即使系统hang的时候hangcheck-timer也不会重启系统。在linux 2.4的内核中，这个缺省值是1；在2.6的内核中，缺省值是0。
当hangcheck_reboot=1并且满足下面的公式时，hangcheck-timer将reboot系统: system hang time > (hangcheck_tick + hangcheck_margin)
All hangcheck-timer defaultvalues should be explicitly overridden when loading the kernel module, based onthe Oracle release as follows:
--所有的hangcheck-timer的参数的缺省值必须在加载内核模块的时候被显式的覆盖，不同的oracle版本可以按照下面来设置：
（1）9i: Assuming thedefault setting of "oracm misscount" is set to 220 seconds:
hangcheck_tick=30hangcheck_margin=180 hangcheck_reboot=1
--9i: 假如"oracle misscount"的缺省设置是220秒，则hangcheck_tick=30hangcheck_margin=1